Hi JakobVoss,
I undid your edit on an item as it changes its scope. If you want to add more statements, it's preferable that a new item is made. Otherwise users who refer to a past version of the item can get confused. I also undid some of your edits as I think they met the definition.
You might want to add "has quality" to describe aspects of identifiers. When reading some of your thesis, I had thought of applying some of its criteria to these.
I could create a new item, and delete or merge the old one but this would not be better. There is no easy answer to semantic change (Q1939117), it always depends on the particular case, so what's wrong with my actual edits?
Merging wouldn't be possible: Help:Merge#Check_to_be_sure.
You removed the info that some of these are actually multi-source.
The current description (there is no definition!) of the item makes no sense. I answered at Talk:Q21264328. Would you prefer to delete the item?